Area Forecast Discussion
Issued by NWS Chicago, IL

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873
FXUS63 KLOT 301926
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
226 PM CDT SAT APR 30 2016

.SHORT TERM...
146 PM CDT

THROUGH SUNDAY...

COOL/CLOUDY/MOIST AIRMASS CONTINUES TO LIFT NORTH ACROSS NORTHERN
IL/NORTHWEST IN THIS AFTERNOON. IR IMAGERY HAD INITIALLY INDICATED
CLOUD TOPS WERE BETWEEN -60 TO -65 DEG C...BUT OVER THE PAST FEW
HOURS CLOUDS HAVE BEEN QUICKLY WARMING WITH TOPS NOW BETWEEN -50
TO -55 DEG C. IN ADDITION A WEDGE OF DRIER AIR CONTINUES TO LIFT
NORTHEAST AS THE AREA OF LOW PRESSURE MOVES INTO SOUTHCENTRAL IOWA
THIS AFTERNOON. THE PRESSURE GRADIENT HAS ARRIVED OVER NORTHERN IL
THIS AFTERNOON WITH EASTERLY WINDS INCREASING TO BETWEEN 10-15KT
AND GUSTS AROUND 20KT. THE LOW WILL BEGIN TO WEAKEN THIS
EVENING...BUT WITH A BROAD RIDGE POSITIONED OVER ONTARIO IT IS
LIKELY THAT THE LOW WILL STALL FROM LIFTING NORTHEAST OVERNIGHT.
THIS WILL SET THE STAGE FOR STEADIER PRECIP TO SHIFT NORTH AND
END LATE THIS AFTERNOON FROM SOUTH TO NORTH...WITH JUST A FEW
LINGERING SHOWERS THROUGH THE OVERNIGHT. THE BAGGY ATMOSPHERE
WILL CONTINUE TO SEE SHALLOW MOISTURE FEED ACROSS THE
REGION...WITH CONSIDERABLY LOWER CEILINGS OVERNIGHT. THE LACK OF A
LIFT WILL KEEP DROPLET SIZE MINIMAL AND LIKELY LEAD TO PATCHY
DRIZZLE/LGT RAIN. TEMPS OVERNIGHT WILL LIKELY NOT CHANGE
MUCH...WITH LOWS IN THE 40S.

WITH THE BROAD SFC RIDGE DISPLACED TO THE NORTH...THIS WILL KEEP
THE WARM FRONTAL BOUNDARY FROM LIFTING TOO FAR NORTH TOWARDS THE
CWFA OVERNIGHT INTO SUNDAY...HOWEVER THE 500MB VORT MAX WILL BE
UPSTREAM ACROSS SOUTHWEST IOWA TO STAR THE DAY SUNDAY. AS THIS
FEATURE PIVOTS NORTHEAST ACROSS NORTHERN IL...FORCING WILL RETURN
WITH INCREASED CHANCES FOR SHOWERS AND PERHAPS AN ISOLATED
THUNDERSTORM SOUTH OF I-80 SUNDAY AFTERNOON. THE NORTHEAST FLOW
OFF OF LAKE MICHIGAN WILL LIKELY KEEP TEMPS AGAIN SUN AFTN IN THE
40S FOR AREAS ADJACENT TO THE LAKE...MEANWHILE FURTHER INLAND
TEMPS SHOULD BE ABLE TO WARM INTO THE LOW/MID 50S. ACROSS THE
SOUTHERN CWFA THE WARM FRONTAL BOUNDARY WILL BE LINGERING NEARBY
WITH TEMPS NEARING THE LOW 60S.

BEACHLER

&&

.LONG TERM...
320 AM CDT

MONDAY THROUGH FRIDAY...

AMPLIFIED AND BLOCKY UPPER AIR PATTERN WILL BE IN PLACE MUCH OF
NEXT WEEK WITH A BLOCKING RIDGE IN PLACE ACROSS THE WESTERN HALF
OF THE CONUS TO START THE WEEK AND NORTHWEST FLOW ACROSS THE
EASTERN CONUS. REGIONALLY...SURFACE HIGH AND NORTHWEST FLOW WILL
PROVIDE DRY CONDITIONS MONDAY WITH SLIGHTLY COOLER THAN NORMAL
TEMPERATURES WITH HIGHS IN THE LOW TO MID 60S INLAND AND LOW 50S
LAKEFRONT...THEN BY TUESDAY EXPECT HIGHS TO BE NEAR THE 70 MARK.
MEANWHILE...WHILE THE UPPER RIDGE IS CENTERED OVER BRITISH
COLUMBIA AND ALBERTA EARLY NEXT WEEK...PORTIONS OF THE JET STREAM
TOP THE RIDGE OVER THE ARCTIC CIRCLE AND WILL DISLODGE A COLD
AIRMASS TOWARDS THE REGION SCHEDULED TO ARRIVE AROUND MIDWEEK.
THERE ARE DIFFERENCES IN THE MAGNITUDE AND SOUTHERN EXTENT OF THE
AIRMASS WITH THE GFS BRINGING AROUND -5C H85 AIR SQUARELY INTO THE
MIDWEST BY EARLY THURSDAY...VERSUS THE ECMWF PROVIDING MORE OF A
GLANCING BLOW OF COLD AIR. THIS RESULTS IN QUITE A BIT OF
UNCERTAINTY FOR TEMPERATURES BEYOND MIDWEEK THOUGH BELOW NORMAL IS
HEAVILY FAVORED...AND CURRENT FORECAST FOR THURSDAY AND FRIDAY MAY
BE TOO WARM IF 00Z MODEL TRENDS HOLD. THERE IS NOT A LOT OF
MOISTURE WITH THE COLD FRONT BUT A SLIGHT/LOW CHANCE OF RAIN IS
WARRANTED WITH FROPA. THE UPPER RIDGE IS PROGGED TO GRADUALLY
SHIFT EAST TOWARDS THE MID SECTION OF THE COUNTRY BY LATE IN THE
WEEK AND AS WE SHOULD SEE DRY WEATHER AND A GRADUAL WARMING TREND
TO CLOSE OUT THE WEEK AND AS WE HEAD INTO INTO NEXT WEEKEND.

DEUBELBEISS

&&

.AVIATION...
FOR THE 18Z TAFS...

MAIN CONCERNS FOR THE REMAINDER OF THE AFTERNOON THROUGH THE
OVERNIGHT HOURS WILL BE ON CIGS AND VSBY REDUCTIONS. CONSIDERABLE
MOISTURE AND RAIN CONTINUES TO FEED NORTH/NORTHEAST ACROSS
NORTHERN IL AND NORTHWEST IN THIS AFTERNOON...WHICH HAS BEEN
STEADILY OVERCOMING THE INITIAL DRY LAYER FROM THIS MORNING. CIGS
HAVE BEEN SLOWLY LOWERING TOWARDS MVFR CONDS...BUT EXPECT CLOSER
TO 00Z CIGS WILL BE FLIRTING WITH IFR CONDS. THE STEADIER PRECIP
SHOULD BE DIMINISHING IN COVERAGE BETWEEN 00-02Z...WITH JUST SOME
LINGERING DZ OR LGT RA THROUGH THIS EVENING. WINDS WILL CONTINUE
FROM THE EAST WITH OCCASIONAL GUSTS BETWEEN 20-24KT THIS
AFTERNOON...THEN DIMINISHING AFTER SUNSET. OVERNIGHT PRECIP
COVERAGE SHOULD END WITH JUST PATCHY DZ REMAINING. THIS IS THE
TIME WHEN GUIDANCE HAS BEEN LEANING HEAVILY TOWARDS CIGS FALLING
FURTHER TOWARDS LIFR CONDS...WITH BASES BETWEEN 200-300FT AGL. IT
IS POSSIBLE A FEW SPOTS COULD GO FURTHER DOWN OVERNIGHT. HELPING
CIGS TO LOWER TONIGHT WILL BE THE LIGHTER WINDS THAT DEVELOP AS
THE LOW PRESSURE APPROACHES THE REGION FROM THE
SOUTHWEST...HOWEVER WIND DIRECTIONS WILL REMAIN NORTHEASTERLY AND
SPEEDS WILL BE BETWEEN 6-12KT.

AFTER DAYBREAK SUNDAY WINDS WILL TURN MORE NORTHERLY...WHICH
SHOULD HELP TO LIFT CIGS SLIGHTLY BACK TOWARDS IFR CONDS. BUT WITH
THE CONTINUED LACK OF STRONG MIXING AND A WEAK PRESSURE GRADIENT
THE CONTINUED IFR/LOW END MVFR CIGS WILL PERSIST WITH A FEW
SHOWERS IN THE AREA.

BEACHLER

&&

.MARINE...
242 AM CDT

AN EXPANSIVE AREA OF HIGH PRESSURE WILL REMAIN NORTH OF THE LAKES
TODAY...AS AN AREA OF LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST INTO THE LOWER MISSOURI VALLEY BY EVENING...AND THEN
TRACKS TO THE EASTERN LAKES/UPPER OHIO VALLEY ON SUNDAY. COOL
NORTHEAST FLOW FROM THE HIGH TO THE NORTH WILL INCREASE ESPECIALLY
ACROSS SOUTHERN LAKE MICHIGAN TODAY AS THE LOW APPROACHES FROM THE
SOUTHWEST AND TIGHTENS UP THE GRADIENT. EAST-NORTHEASTERLY FLOW AT
20-25 KT WILL PRODUCE SMALL CRAFT ADVISORY CONDITIONS ON SOUTHERN
LAKE MICHIGAN...LIKELY LINGERING THROUGH SUNDAY AS WINDS BACK MORE
NORTHERLY AND THE FETCH LENGTHENS. WEAK HIGH PRESSURE WILL SPREAD
ACROSS THE LAKES MONDAY ALLOWING WINDS AND WAVES TO SUBSIDE.
ANOTHER ROUND OF MODESTLY STRONG NORTH WINDS APPEARS LIKELY MID-
WEEK.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 1 AM
     MONDAY.

&&

$$

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